1. Field of the Invention
The present invention relates to a ballast control IC, particularly for driving fluorescent lamps, and more particularly to a ballast control IC with an operational amplifier incorporated into the ballast control IC.
2. Related Art
Electronic ballasts for gas discharge circuits have come into widespread use, at least in part to the availability of power MOSFET switching devices and insulated gate bipolar transistors (IGBTs) that can replace previously used power bipolar switching devices. A number of integrated circuits have been devised for driving the gates of power MOSFETs or IGBTs in electronic ballasts. Some examples include the IR2155, IR2157, IR21571 and IR2167 products which are sold by International Rectifier Corporation, the assignee of the present application. These products are further described in U.S. Pat. Nos. 5,545,955 and 6,211,623 the disclosures of which are hereby incorporated by reference herein.
One of the features that is useful in electronic ballasts is the ability to dim the fluorescent lamp. While IC control circuits have been introduced that include this feature, such circuits provide only a very specific manner of achieving ballast control. That is, these conventional control IC's lack flexibility. For example, the IR21592, another product of the assignee, International Rectifier Corporation, provides for dimming of a fluorescent lamp, however, dimming is accomplished by means of phase control regulation. While this solution provides adequate dimming, the function of the IC remains limited.
Thus, it would be desirable to provide a control IC for a ballast with increased flexibility that allows for increased functionality such as by including an operational amplifier that is integrated directly into the IC to provide for dimming or other functionality.